This section provides background information related to the present disclosure which is not necessarily prior art.
A laser powder-bed fusion additive manufacturing (“PBFAM”) process produces metal parts through layer-by-layer deposition of powdered metal feed materials. The design freedom afforded by this process, however, is complicated by the process complexity. It has been determined that there are over 130 different parameters that may potentially affect the part building process in a typical PBFAM process. Only the optimal selection and/or control of these parameters results in part production that is free, to an acceptable level, of defects, residual stresses and deformations.
Numerical modeling is a powerful tool to find the optimal manufacturing parameters for specific parts and materials. Today, modeling includes consideration of a plurality of highly important physical processes, for example, laser melting of the powdered material, the melt pool structure including the melt motion under the effect of capillary forces and the recoil momentum, melt evaporation of the powdered material, etc. But in practically all models, the absorption of laser light by the powdered feed material is treated as a surface one with constant absorptivity.
The powerful laser absorption by the powdered metal feed material is a complex process that is influenced by a wide variety of physical effects. The laser is capable of melting both the thin layer of powdered feed material and a substrate supporting the powdered feed material. The melt surface of the powdered feed material that the laser interacts with is in effect “non-stationary modulated” due to the melt motion, which affects the absorptivity of the powdered feed material. At higher intensities, when the recoil momentum digs out an open channel, sometimes referred to as a “key hole”, light interacts with the key hole walls and ejected vapors. Consistent and accurate modeling of these complex effects is extremely difficult, if not impossible. Additionally, for the modeling of microstructure and residual stresses, one would need only the energy deposited to the substrate (i.e., the powdered metal feed material). And as part of the absorbed energy is ejected with the vapors and part of the laser light is absorbed in the vapor plume, the percentage of absorbed laser light is very difficult to model.
Yet another variable that complicates obtaining consistent performance with a PBFAM manufacturing process is the drift of various components used in the process over time. For example, thermal effects due to the optics contamination can change the laser beam parameters non-uniformly over a production table as the beam is scanned. In addition, the thickness and composition of the powdered feed material being used can change slightly from one batch of feed material to the next.
The foregoing factors all serve to make self-consistent modeling of absorptivity when performing a PBFAM manufacturing operation out of the reach of present day modeling techniques.